THE MANUFACTURE OF ENZYMS 



93 



alimentary tract organized to deal properly with each 

 class of food. 



The Manufacture of Enzyms. — The method of 

 digestion, as stated previously (see Chap. VII), is to 

 bring in contact with the food a particular kind of sub- 

 stance known as an enzym, which has the special property 

 of hastening the decomposition of the complex food 

 material into the simpler substances which we call the 

 digestion ^products. Different kinds of enzyms must be 

 provided for the different food constituents. In the 

 higher animals the enzyms are manufactured, as pre- 

 viously stated, by groups of living cells which have that 

 as their special function and which we call secreting 



Fig. 19. — Diagram of a Simple Gland. The secreting cells (a) 

 make up a tube, closed at the bottom, opening at the top into the 

 alimentary canal. Surrounding this tube is a network of fine blood- 

 vessels (c). In the spaces between the blood vessels and the gland 

 there is tissue fluid. 



glands (Fig. 19). These glands withdraw from the tissue 

 fluid which surrounds them various food constituents; 

 their functional metabolism consists in manufacturing 

 out of this material the special substances which serve 

 as enzyms. These latter are poured out along with a 

 stream of water from the gland into the alimentary tract, 

 where the enzym becomes mixed with the food. The 

 most famihar example of this is the saliva, which is 

 manufactured by the salivary glands, poured out into the 

 mouth, and there mixed with the food as it is being 

 chewed. 



